Yeah - I've had the same positive experiences with the HK powersellers on ebay.
And great customer service for the one thing that didn't work (a six-cell battery for Dell Mini9): gave me a full refund and didn't even ask me to ship the dud back.
I remember looking at a iPhone car charger for $19.99 at a Canadian retailer (The Source, maybe?), and the packaging had a manufacturer name on it. After some Googling and digging, I found the manufacturer's page for placing orders. In lots of 100, the price was like $1.64 or something like that; and when you got up to 1000, it was below $1.
I'm sure all of the stuff like memory cards come off the same assembly lines; it's the labels and packaging that costs the big $$.
I'd be surprised if you didn't get a good product; and if you do get a dud, I bet they'll replace it for you quickly. $23 for 16GB is a good price, but not absurdly low.
(It does lead one to ask, though, how/why Apple charges a $100 premium to go from a 16GB to 32GB iPod or iPad.......oh right - because they can, and people will pay it.